In the current environmental climate, energy needs to be conserved and recycled as much as possible to prevent wastage - every joule saved means less fossil fuel burnt. Harvesting waste energy has become a popular target for researchers and scientists, who are coming up with innovative techniques to achieve this. One of the most promising is nanotechnology-based thermoelectric devices, which look to be a promising approach to save energy.
What is Thermoelectricity?
The direct conversion of heat into electricity, or electricity into heat, is known as thermoelectricity. This conversion process is referred to as the Peltier-Seebeck effect. This effect is name after two physicists - Jean Peltier and Thomas Seebeck. Peltier discover that current sent into two different electrical conductors that are connected at two junctions will result in heating up of one junction while the other junction cools down. Peltier went on to demonstrate that a drop of water can be made to freeze at a bismuth-antimony (BiSb) junction by just reversing the current. Peltier also discovered that electric current can be made to flow when a temperature difference is placed across a junction of different conductors.
Role of Nanotechnology in Thermoelectric Devices
Thermoelectricity is an extremely interesting source of electric power because of its ability to convert heat flow directly into electricity. Thermoelectric devices are energy converters that are easily scalable and have no moving parts or liquid fuels, making them applicable in almost any situation where large quantities of heat tend to go to waste, from clothing to large industrial facilities.
A number of research groups have been investing their efforts in finding the perfect material with appropriate properties to create an efficient thermoelectric effect, and nanomaterials seem to fit the bill. Whilst thermoelectric materials have been known and understood for quite some time, they have so far not been efficient enough to use commerically. With the advent of nanotechnology, however, that is changing.
Nanostructures used in materials will help maintain good electrical conductivity and reduce thermal conductivity. The performance of thermoelectric devices can thus be enhanced with the use of nanotechnology-based materials that have improved thermoelectric properties and good solar energy absorption abilities.
Thermoelectric materials based on bismuth telluride stand out as perfect examples highlighting the role of nanomaterials for thermoelectric devices. Bismuth telluride materials are best suited for room temperature applications with ZT (figure of merit) of ~1. The usage of nanostructured materials and low dimensional superlattice structures has lead to improvements in ZT. The usage of nanostructures smaller than the wavelength of light enhances the scattering of photons and thus decreases thermal conductivity. This decrease in thermal conductivity seems to be the most vital benefit of nanostructuring for thermoelectric materials.
A good thermoelectric material will thus have very poor thermal conductivity, but a very good electrical conductivity. Carbon nanotubes and graphene as thermoelectric materials exhibit improved thermoelectric properties. Further applications of nanostructuring can help improve scaling and optimization of thermoelectric devices that can be used to decrease carbon dioxide emissions and improve energy efficiency.
Applications of Thermoelectricity
The applications of thermoelectricity are given below:
- Power suppliers and sensors in band aids
- Burning oil lamp driving a wireless receiver for remote communications
- Pwering small electronic devices like MP3 players, digital watches, GPS/GSM chips and pulse meters with body heat
- Rapidly cooling seats in luxury cars.
- Harvesting waste heat in cars by converting it into electricity
- Converting waste heat in factories or industrial facilities into additional power
- Solar thermoelectrics could be more efficient than photovoltaics for generating electricity, particularly in regions with less direct sunlight.
Researchers have recently highlighted the need to reduce the wastage of heat by storing and reusing the energy, harnessing the heat to produce electricity and therefore recycling the energy that would be wasted. To carry this out, researchers suggest the use of thermoelectric materials, which directly produce electricity from a temperature gradient. The use of nanotechnology in designing these materials will improve the performance of these materials and also improve energy efficiency.
Experts from Cranfield University recently conducted research on the various applications of nanomaterials in the environment and energy sectors. The use of thermoelectric and solar absorbing materials as energy generation technologies is the most researched topic currently. A professor from this university highlighted the use of these two materials to form one device that will have the ability to generate from the thermoelectric effect.
One of the proposed uses of these efficient, nanotechnology-enhanced thermoelectric devices focuses on reducing the load of batteries carried by soldiers in the battlefield. This will help increasing the range of the soldiers and allow them to carry more ammunition and food and stay away from base for longer time periods.
With the demand for energy increasing in all aspects of life from offices to households to battlefields, the need to implement nanotechnology-based solutions like thermoelectric devices is gaining importance. Implementation of nanotech-based thermoelectric devices will prevent wastage of energy and make way for better energy recycling and energy saving measures.
Sources and Further Reading